A computer system with redundancy based on multiple networks achieves a high availability as such computer system can be operated by using an alternative network when a failure occurs. Also, such computer system can achieve load balancing and thereby offer a high speed communication in a normal operation by selecting networks actually used for the communications from multiple networks.
In order to provide efficient communications in a system, it is necessary to use networks with high performances as preferentially as possible. For instance, it is possible to improve the communication efficiency by selecting routes to be used on the basis of performance information of communication lines.
A system which selects routes to be used on the basis of performance information is disclosed, for example, in Japanese Patent Application Publication No. 2007-189615, (see patent literature 1). The system disclosed in patent literature 1 configures efficient communication routes by calculating routes on the basis of the network load.
A network monitoring assistance apparatus disclosed in patent literature 1 detects a failure by monitoring network appliances and analyses the affected range of the failure to calculate communication routes which bypass the affected range. In this operation, the network monitoring assistance apparatus calculates the routes on the basis of the utilization status of the traffic and the network load, including CPU utilization ratios and the like.
The system disclosed in patent literature 1 configures routes to be used on the basis of the utilization status of the traffic so that the communication routes bypass the affected range of the failure. Accordingly, the system can select a route with a low traffic utilization ratio, bypassing the failure. A route which is currently out of operation may be selected as a route to be used since no traffic occurs through the route; however, the route thus selected does not always offer a high transfer performance. Accordingly, no consideration is paid to immediate recovery in case of occurrence of an entire-Network failure in the system disclosed in patent literature 1.
Other examples of computer systems are disclosed in Japanese Patent Application Publication No. 2000-348005 A (patent literature 2) and Japanese Patent Application Publication No. 2007-287064 A (patent literature 3). Patent literatures 2 and 3 disclose storage systems incorporating multiple routes, which offer an improved availability and performance by dynamically switching paths to be used in accordance with the load status and the failure occurrence status.